Digital subscriber line (Digital Subscriber Line, DSL for short) is a high speed data transmission technology in an unshielded twisted pair (Unshielded Twisted Pair, UTP for short) transmission. Various types of DSLs may be collectively referred to as an xDSL. Apart from a DSL using baseband transmission, the xDSL using passband transmission enables, by using a frequency division multiplexing technology, the xDSL to coexist with a plain old telephone service (Plain Old Telephone Service, POTS for short) in the same twisted pair. The xDSL occupies a high frequency band, and the POTS occupies a baseband part smaller than 4 kHz. A DSL access multiplexer (DSL Access Multiplexer, DSLAM for short) can provide access services for multiple xDSLs.
When a user subscribes to an xDSL service, line activation rate should be considered. That is, at an office, the xDSL service cannot be normally provisioned in all user twisted pairs. The main cause of the line activation rate problem is as follows: Due to electromagnetic induction, interference, which is also referred to as crosstalk (Crosstalk), occurs between multiple DSL signals accessed by the DSLAM. The crosstalk includes near-end crosstalk (near-end crosstalk, NEXT for short) and far-end crosstalk (far-end crosstalk, FEXT for short). Because energy of the crosstalk is enhanced with the increase of a frequency band, the far-end crosstalk affects the transmission performance of a line more seriously with the increase of the frequency band used by the xDSL. Therefore, when multiple users in one cable binder request to subscribe to the xDSL service, the far-end crosstalk brings about such problems to some lines as low rate, unstable performance, and even service provision failure, and finally causes a problem of low line activation rate. For lines where the xDSL service cannot be provisioned, an operator needs to perform troubleshooting. This process needs to consume a lot of human and material resources, which greatly increases operation costs of the operator. Therefore, a single end line test (Single End Line Test, SELT for short) technology is emerging. The SELT is a technology used to perform testing, checking, and fault locating on a line in an automatic test manner.
During the implementation of the present invention, the inventor discovers that the prior art has at least the following problems:
An SELT test signal is generally sent within a relatively wide spectrum range, and the sent signal imposes crosstalk on neighboring lines, leading to problems such as generation of bit errors in the neighboring lines or even offline in severe cases.